A Theory for Stethoscope Acoustics
* Presenting author
Maximising the signal to noise ratio while considering ergonomics and aesthetics is the key design challenge for modern stethoscopes. In order to optimise the design, there is a need for a well-validated model for the transfer function from a source within the chest to the output signal obtained.Most variants of the stethoscope are air-coupled sensors. Here we propose a new theory for the acoustics of this type of sensor, which takes into account the coupling between the sensor and the human chest. We have conducted a rigorous experimental campaign to characterise the transfer function of the chest-stethoscope system and have investigated the effects of key design parameters. Our data confirms traditional findings on the effects of bell geometry and diaphragm usage, but also highlights the importance of the coupling between the sensor and the chest, and reveals features of the transfer function that are not captured by existing models.Our model employs a transmission matrix formulation and discretises the system into lumped element components. It can be used to inform design choices for acoustic, electronic and dual-mode stethoscopes, opening up the possibility of an optimum design that maximises the signal to noise ratio for a desired application.